For the ATX standard of motherboard, one characteristic thereof is that, except the DC power (3.3 V, 5 V, 12 V . . . ) provided during operation, a standby power system is also provided for supplying a starting power to the computer host, no matter the computer is under operation or shutdown.
For the current computer technology, except the operating system and other applications, there still has many external electronic devices which are operated independently as the computer host is shutdown, for example, speaker, night light, playing music CD directly through the panel of CD-ROM drive, mobile phone charging socket, etc., can be independently operated under shutdown situation, or a small LED mounted on the computer case for displaying information of temperature, humidity, time, or a bright and dazzling computer case with an illuminating efficiency.
However, the personal computer in the market seems to lack these functions. The reason is the space inside the computer host is extremely limited so that it is always insufficient to install additional power supplying module after installing the inner electronic devices, such as hard disk drive, CD-ROM drive, motherboard . . . , etc. Further, for utilizing the standby power from the power supply after shutdown, the panel of the case must be opened for installing extra sockets, and additional power lines have to be disposed inside the computer host for providing the DC power from the standby power to the external electronic devices which are connected to the sockets. But, it is obvious that the ideas described above diverge from the trends of compact volume, organized inner cable, and simplified case panel which are used for current personal computer.
Furthermore, the current personal computer always has the USB interface disposed thereon. Generally, except being used for data transmission, the USB interface also provides a 5 V DC power. However, after the computer is shutdown, the power transmission is also stopped. Therefore, if the original USB interface (or other available buses, such as IEEE 1394 bus interface) can be utilized to provide the DC power no matter the computer is under operation or shutdown, then the external electronic devices with the corresponding USB connector can directly draw the DC power from the USB interface on the computer host, so that the convenience can be improved and the problem of insufficient space also can be solved.